1. Field of the Invention
The present invention relates to detection circuits, and particularly to a zero-crossing point detection circuit.
2. Description of Related Art
Zero-crossing point detection circuits are well known for detecting the instances at which a signal voltage changes from negative to positive and from positive to negative, such as in uninterrupted power supply (UPS) system, or the like.
Generally speaking, such a zero-crossing point detection circuit includes a level comparator circuit consisting of a differential operational amplifier of high gain, some resistors, and some capacitors. However, zero-crossing point detection circuits are directly connected to a power switch circuit and thus are susceptible to static jamming, coupling jamming and the like. Furthermore, the comparator circuit is a simulation circuit which is very complicated to select proper resistors and capacitors.
What is desired, therefore, is to provide a zero-crossing point detection circuit resistant to noise jamming.